Here's our final daily composite of the six major national tracking polls. Many national polls have coalesced around a projected 52% popular-vote share for Barack Obama, and it shows in our composite:

• Gallup: Obama 53%, McCain 42%, with a ±2% margin of error, compared to a 52%-43% lead from yesterday.

• Rasmussen: Obama 52%, McCain 46%, with a ±2% margin of error, compared to a 51%-46% Obama lead from yesterday.

• ABC/Washington Post: Obama 53%, McCain 44%, with a ±2% margin of error, compared to a 54%-43% Obama lead yesterday

• Hotline/Diageo: Obama 50%, McCain 45%, with a ±3.3% margin of error, unchanged from yesterday.

• Research 2000: Obama 51%, McCain 45%, with a ±3% margin of error, compared to a 51%-44% Obama lead from yesterday.

• Zogby: Obama 51%, McCain 44%, with a ±2.9% margin of error, compared to a 50%-44% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.9%-44.3%, a lead of 7.6 points, compared to the 51.5%-44.2% Obama lead from yesterday.

Counting today, Obama's lead has increased by small amounts in the last five consecutive Composites.

Most elections conclude with a tightening of the race, as the underdog picks up some final bit of steam. But this one seems to have been an exception -- McCain began closing the gap, but then Obama just pulled away all over again.

One more important poll is due tomorrow. We'll be live-blogging it when it comes out.

Here's our daily composite of the six major national tracking polls. Barack Obama's lead is continuing to inch upwards in the daily tracking polls, undoing much of the progress that John McCain made about a week ago:

• Gallup: Obama 52%, McCain 43%, with a ±2% margin of error, compared to a 52%-42% lead from yesterday.

• Rasmussen: Obama 51%, McCain 46%, with a ±2% margin of error, unchanged from yesterday.

• ABC/Washington Post: Obama 54%, McCain 43%, with a ±2% margin of error, compared to a 53%-44% Obama lead yesterday

• Hotline/Diageo: Obama 50%, McCain 45%, with a ±3.3% margin of error, compared to a 51%-44% Obama lead from yesterday.

• Research 2000: Obama 51%, McCain 44%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 50%, McCain 44%, with a ±2.9% margin of error, compared to a 49%-44% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.5%-44.2%, a lead of 7.3 points, compared to the 51.2%-44.1% Obama lead from yesterday. Counting today, Obama's lead has increased by small amounts in the last four consecutive Composites.

Here's our daily composite of the six major national tracking polls. Barack Obama's lead expanded slightly again today, as most pollsters show him pulling away from John McCain in the home stretch:

• Gallup: Obama 52%, McCain 42%, with a ±2% margin of error, compared to a 52%-43% lead from yesterday.

• Rasmussen: Obama 51%, McCain 46%, with a ±2% margin of error, compared to a 51%-47% Obama lead from yesterday.

• ABC/Washington Post: Obama 53%, McCain 44%, with a ±2.5% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 51%, McCain 44%, with a ±3.3% margin of error, compared to a 48%-41% Obama lead from yesterday.

• Research 2000: Obama 51%, McCain 44%, with a ±3% margin of error, compared to a 51%-45% Obama lead yesterday.

• Zogby: Obama 49%, McCain 44%, with a ±2.9% margin of error, compared to a 50%-43% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.2%-44.1%, a lead of 7.1 points, compared to the 51.0%-44.1% Obama lead from yesterday. Obama's lead also increased in yesterday's Composite, as well as in the one before that.

Here's our daily composite of the six major national tracking polls. Barack Obama lead is steadily ticking back up again, suggesting that the recent period in which the race was starting to tighten may be over:

• Gallup: Obama 52%, McCain 43%, with a ±2% margin of error, compared to a 51%-44% lead from yesterday.

• Rasmussen: Obama 51%, McCain 47%, with a ±2% margin of error, compared to a 51%-46% Obama lead from yesterday.

• ABC/Washington Post: Obama 53%, McCain 44%, with a ±2.5% margin of error, compared to a 52%-44% Obama lead from yesterday.

• Hotline/Diageo: Obama 48%, McCain 41%, with a ±3.3% margin of error, compared to a 48%-42% Obama lead from yesterday.

• Research 2000: Obama 51%, McCain 45%, with a ±3% margin of error, compared to a 50%-45% Obama lead yesterday.

• Zogby: Obama 50%, McCain 43%, with a ±2.9% margin of error, unchanged from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.0%-44.1%, a lead of 6.9 points, compared to the 50.5%-44.2% Obama lead from yesterday. Obama's lead also increased in yesterday's Composite.

Here's our daily composite of the six major national tracking polls. The recent tightening in the race appears to have stopped for today, with Obama's lead expanding slightly:

• Gallup: Obama 51%, McCain 44%, with a ±2% margin of error, unchanged from yesterday.

• Rasmussen: Obama 51%, McCain 46%, with a ±2% margin of error, compared to a 50%-47% Obama lead from yesterday.

• ABC/Washington Post: Obama 52%, McCain 44%, with a ±2.5% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 48%, McCain 42%, with a ±3.3% margin of error, compared to a 49%-42% Obama lead from yesterday.

• Research 2000: Obama 50%, McCain 45%, with a ±3% margin of error, compared to a 50%-44% Obama lead yesterday.

• Zogby: Obama 50%, McCain 43%, with a ±2.9% margin of error, compared to a 49%-44% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.5%-44.2%, a lead of 6.3 points, compared to the 50.2%-44.4% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama's support may have dipped slightly in today's polling as the race slowly tightens, but John McCain has failed to make new headway and Obama remains ahead:

• Gallup: Obama 51%, McCain 44%, with a ±2% margin of error, unchanged from yesterday.

• Rasmussen: Obama 50%, McCain 47%, with a ±2% margin of error, compared to a 51%-46% Obama lead from yesterday.

• ABC/Washington Post: Obama 52%, McCain 44%, with a ±2.5% margin of error, compared to a 52%-45% Obama lead from yesterday.

• Hotline/Diageo: Obama 49%, McCain 42%, with a ±3.3% margin of error, compared to a 50%-42% Obama lead from yesterday.

• Research 2000: Obama 50%, McCain 44%, with a ±3% margin of error, compared to a 50%-43% Obama lead yesterday.

• Zogby: Obama 49%, McCain 44%, with a ±2.9% margin of error, compared to a 49%-45% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.2%-44.4%, a lead of 5.8 points, compared to the 50.6%-44.4% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. John McCain has chipped away slightly at Barack Obama's lead in today's polls, but Obama is still ahead and remains at over 50% support:

• Gallup: Obama 51%, McCain 44%, with a ±2% margin of error, compared to a 53%-43% Obama lead from yesterday.

• Rasmussen: Obama 51%, McCain 46%, with a ±2% margin of error, unchanged from yesterday.

• ABC/Washington Post: Obama 52%, McCain 45%, with a ±2.5% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 50%, McCain 42%, with a ±3.3% margin of error, unchanged from yesterday.

• Research 2000: Obama 50%, McCain 43%, with a ±3% margin of error, compared to a 50%-42% Obama lead yesterday.

• Zogby: Obama 49%, McCain 45%, with a ±2.9% margin of error, compared to a 50%-45% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.6%-44.4%, a lead of 6.2 points, compared to the 51.2%-44.0% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. John McCain has picked up some of the undecided vote, but Barack Obama's support is steady and he remains well ahead nationally:

• Gallup: Obama 53%, McCain 43%, with a ±2% margin of error, compared to a 52%-43% Obama lead from yesterday.

• Rasmussen: Obama 51%, McCain 46%, with a ±2% margin of error, compared to a 52%-44% Obama lead from yesterday.

• ABC/Washington Post: Obama 52%, McCain 45%, with a ±2.5% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 50%, McCain 42%, with a ±3.6% margin of error, unchanged from yesterday.

• Research 2000: Obama 50%, McCain 42%, with a ±3% margin of error, compared to a 51%-40% Obama lead yesterday.

• Zogby: Obama 50%, McCain 45%, with a ±2.9% margin of error, compared to a 49%-44% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.2%-44.0%, a lead of 7.2 points, compared to the 51.2%-43.1% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama is still way ahead nationally, with his overall lead dipping just slightly from yesterday:

• Gallup: Obama 52%, McCain 43%, with a ±2% margin of error, compared to a 51%-44% Obama lead from yesterday.

• Rasmussen: Obama 52%, McCain 44%, with a ±2% margin of error, unchanged from yesterday.

• ABC/Washington Post: Obama 52%, McCain 45%, with a ±2.5% margin of error, compared to a 53%-44% Obama lead from yesterday.

• Hotline/Diageo: Obama 50%, McCain 42%, with a ±3.3% margin of error, compared to a 50%-43% Obama lead from yesterday.

• Research 2000: Obama 51%, McCain 40%, with a ±3% margin of error, compared to a 52%-40% Obama lead yesterday.

• Zogby: Obama 49%, McCain 44%, with a ±2.9% margin of error, compared to a 51%-42% Obama lead from yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.2%-43.1%, a lead of 8.1 points, compared to the 51.6%-42.8% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama already-solid national lead may be inching up even further:

• Gallup: Obama 51%, McCain 44%, with a ±2% margin of error, compared to a 51%-45% Obama lead yesterday.

• Rasmussen: Obama 52%, McCain 44%, with a ±2% margin of error, compared to a 52%-45% Obama lead from yesterday.

• ABC/Washington Post: Obama 53%, McCain 44%, with a ±2.5% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 50%, McCain 43%, with a ±3.3% margin of error, unchanged from yesterday.

• Research 2000: Obama 52%, McCain 40%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 51%, McCain 42%, with a ±2.9% margin of error, compared to a 51%-41% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.6%-42.8%, a lead of 8.8 points, compared to the 51.6%-43.1% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama is essentially maintaining his big lead in the polls:

• Gallup: Obama 51%, McCain 44%, with a ±2% margin of error, compared to a 51%-45% Obama lead yesterday.

• Rasmussen: Obama 52%, McCain 45%, with a ±2% margin of error, unchanged from yesterday.

• ABC/Washington Post: Obama 53%, McCain 44%, with a ±2.5% margin of error, compared to a 54%-43% Obama lead from yesterday.

• Hotline/Diageo: Obama 50%, McCain 43%, with a ±3.4% margin of error, compared to a 48%-43% Obama lead from yesterday.

• Research 2000: Obama 52%, McCain 40%, with a ±3% margin of error, compared to a 51%-41% Obama lead from yesterday.

• Zogby: Obama 51%, McCain 41%, with a ±2.9% margin of error, compared to a 52%-40% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.6%-43.1%, a lead of 8.5 points, compared to the 51.5%-43.1% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama's already-big lead has inched up again:

• Gallup: Obama 51%, McCain 45%, with a ±2% margin of error, compared to a 52%-44% Obama lead yesterday.

• Rasmussen: Obama 52%, McCain 45%, with a ±2% margin of error, compared to a 51%-45% Obama lead from yesterday.

• ABC/Washington Post: Obama 54%, McCain 43%, with a ±2.5% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 48%, McCain 43%, with a ±3.4% margin of error, compared to a 47%-42% Obama lead from yesterday.

• Research 2000: Obama 51%, McCain 41%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 52%, McCain 40%, with a ±2.9% margin of error, compared to a 52%-42% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.5%-43.1%, a lead of 8.4 points, compared to the 51.3%-43.1% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama's lead just keeps getting bigger:

• Gallup: Obama 52%, McCain 44%, with a ±2% margin of error, compared to a 52%-42% Obama lead yesterday.

• Rasmussen: Obama 51%, McCain 45%, with a ±2% margin of error, compared to a 50%-46% Obama lead from yesterday.

• ABC/Washington Post: Obama 54%, McCain 43%, with a ±2.5% margin of error, compared to a 53%-44% Obama lead yesterday.

• Hotline/Diageo: Obama 47%, McCain 42%, with a ±3.4% margin of error, compared to a 47%-41% Obama lead from yesterday.

• Research 2000: Obama 51%, McCain 41%, with a ±3% margin of error, compared to a 50%-42% Obama lead from yesterday.

• Zogby: Obama 52%, McCain 42%, with a ±2.9% margin of error, compared to a 50%-42% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 51.3%-43.1%, a lead of 8.2 points, compared to the 50.5%-43.1% Obama lead from yesterday.

Here's our daily composite of the six major national tracking polls. Barack Obama continues to lead John McCain by a healthy margin, with a slight dip in McCain's support today:

• Gallup: Obama 52%, McCain 42%, with a ±2% margin of error, compared to a 52%-43% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 46%, with a ±2% margin of error, unchanged from yesterday.

• ABC/Washington Post: Obama 53%, McCain 44%, with a ±3% margin of error, the same as yesterday's numbers. This is the second day of the ABC/WaPo tracking poll, and the first day we're including it in the Composite.

• Hotline/Diageo: Obama 47%, McCain 41%, with a ±3.4% margin of error, compared to a 47%-42% Obama lead from yesterday.

• Research 2000: Obama 50%, McCain 42%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 50%, McCain 42%, with a ±2.9% margin of error, compared to a 50%-44% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.5%-43.1%, a lead of 7.4 points, compared to the 50.5%-43.7% Obama lead from yesterday, when the ABC/WaPo numbers are included in yesterday's total.

Here's our daily composite of the five major national tracking polls. Barack Obama continues to lead John McCain by a healthy margin, with a slight expansion of the lead in today's numbers:

• Gallup: Obama 52%, McCain 43%, with a ±2% margin of error, compared to a 51%-44% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 46%, with a ±2% margin of error, compared to a 51%-45% Obama lead from yesterday.

• Hotline/Diageo: Obama 47%, McCain 42%, with a ±3.4% margin of error, compared to a 48%-41% Obama lead from yesterday.

• Research 2000: Obama 50%, McCain 42%, with a ±3% margin of error, compared to the 50%-43% Obama lead from yesterday.

• Zogby: Obama 50%, McCain 44%, with a ±2.9% margin of error, compared to a 48%-45% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.1%-43.7%, a lead of 6.4 points, compared to the 49.9%-43.9% Obama lead from yesterday.

Here's our daily composite of the five major national tracking polls. Barack Obama is holding a sizable lead over John McCain, and has slightly expanded it after a momentary dip yesterday:

• Gallup: Obama 51%, McCain 44%, with a ±2% margin of error, compared to a 50%-46% Obama lead yesterday.

• Rasmussen: Obama 51%, McCain 45%, with a ±2% margin of error, compared to a 50%-45% Obama lead from yesterday.

• Hotline/Diageo: Obama 48%, McCain 41%, with a ±3.4% margin of error, compared to a 49%-42% Obama lead from yesterday.

• Research 2000: Obama 50%, McCain 43%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 48%, McCain 45%, with a ±2.9% margin of error, compared to a 48%-44% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 49.9%-43.9%, a lead of six points, compared to the 49.5%-44.3% Obama lead from yesterday.

Note that this is the first day of polling taken entirely after Wednesday's debate. The pre-debate baseline was an Obama lead of 50.3%-43.7%, meaning that McCain has barely made a dent since then.

Here's our daily composite of the five major national tracking polls. The presidential race may be starting to tighten up as we head into the final two weeks of the campaign, though Barack Obama is still ahead for now:

• Gallup: Obama 50%, McCain 46%, with a ±2% margin of error, compared to a 51%-45% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 45%, with a ±2% margin of error, compared to a 50%-46% Obama lead from yesterday.

• Hotline/Diageo: Obama 49%, McCain 42%, with a ±3.5% margin of error, compared to a 50%-40% Obama lead from yesterday.

• Research 2000: Obama 50%, McCain 43%, with a ±3% margin of error, compared to a 52%-42% Obama lead from yesterday.

• Zogby: Obama 48%, McCain 44%, with a ±2.9% margin of error, compared to a 49%-44% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 49.5%-44.3%, a lead of 5.2 points, compared to the 50.4%-43.9% Obama lead from yesterday.

Here's our daily composite of the five major national tracking polls. With one day of post-debate sampling now incorporated into the three-day tracking poll, there hasn't been much of a change so far in Barack Obama's big lead:

• Gallup*: Obama 51%, McCain 45%, with a ±2% margin of error, unchanged from yesterday.

• Rasmussen: Obama 50%, McCain 46%, with a ±2% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 50%, McCain 40%, with a ±3.4% margin of error, compared to a 49%-41% Obama lead from yesterday.

• Research 2000: Obama 52%, McCain 42%, with a ±3% margin of error, compared to a 52%-41% Obama lead from yesterday.

• Zogby: Obama 49%, McCain 44%, with a ±2.9% margin of error, compared to a 49%-43% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.4%-43.9%, a lead of 6.5 points, pretty much the same as the 50.3%-43.7% Obama lead from yesterday.

*ed. note: Gallup has begun offering two different sub-samples of likely voters, one using a traditional likely-voter model and the other using a modified likely-voter model for an expected higher turnout. For all our composites and Poll Tracker entries, we will be using that second model under the expectation that newly-registered voters and other factors will contribute to a higher turnout this cycle.

Here's our daily composite of the five major national tracking polls. Going into last night's debate, Barack Obama's big lead over John McCain may have been narrowing a bit, though he was still solidly ahead:

• Gallup*: Obama 51%, McCain 45%, with a ±2% margin of error, compared to a 52%-44% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 46%, with a ±2% margin of error, compared to a 50%-45% Obama lead from yesterday.

• Hotline/Diageo: Obama 49%, McCain 41%, with a ±3.4% margin of error, unchanged from yesterday.

• Research 2000: Obama 52%, McCain 41%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 49%, McCain 43%, with a ±2.9% margin of error, compared to a 48%-44% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.3%-43.7%, a lead of 6.6 points, compared to the 50.3%-43.3% Obama lead from yesterday. Two days ago, Obama's composite lead was 50.6%-43.1%.

Remember that this polling was all done before last night's debate, so it doesn't tell us about the post-debate environment. Instead, it gives us a baseline against which we can measure the changes in the coming days.

*ed. note: Gallup has begun offering two different sub-samples of likely voters, one using a traditional likely-voter model and the other using a modified likely-voter model for an expected higher turnout. For all our composites and Poll Tracker entries, we will be using that second model under the expectation that newly-registered voters and other factors will contribute to a higher turnout this cycle.

Here's our daily composite of the five major national tracking polls. Barack Obama is holding on to his big lead over John McCain, which has remained relatively unchanged since the financial meltdown became big news:

• Gallup*: Obama 52%, McCain 44%, with a ±2% margin of error, compared to a 53%-43% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 45%, with a ±2% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 49%, McCain 41%, with a ±3.4% margin of error, compared to a 48%-42% Obama lead from yesterday.

• Research 2000: Obama 52%, McCain 41%, with a ±3% margin of error, unchanged from yesterday.

• Zogby: Obama 48%, McCain 44%, with a ±2.9% margin of error, compared to a 49%-43% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.3%-43.3%, a lead of seven points, compared to a 50.6%-43.1% Obama lead from yesterday.

*ed. note: Gallup has begun offering two different sub-samples of likely voters, one using a traditional likely-voter model and the other using a modified likely-voter model for an expected higher turnout. For all our composites and Poll Tracker entries, we will be using that second model under the expectation that newly-registered voters and other factors will contribute to a higher turnout this cycle.

Here's our daily composite of the five major national tracking polls. Barack Obama's big lead over John McCain is the same as it was yesterday:

• Gallup*: Obama 53%, McCain 43%, with a ±2% margin of error, compared to a 53%-43% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 45%, with a ±2% margin of error, unchanged from yesterday.

• Hotline/Diageo: Obama 48%, McCain 42%, with a ±3.4% margin of error, unchanged from yesterday.

• Research 2000: Obama 52%, McCain 41%, with a ±3% margin of error, compared to a 52%-40% Obama lead from yesterday.

• Zogby: Obama 49%, McCain 43%, with a ±2.9% margin of error, compared to a 48%-44% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.6%-43.1%, a lead of 7.5 points, identical to the 50.6%-43.1% Obama lead from yesterday.

*ed. note: Gallup has begun offering two different sub-samples of likely voters, one using a traditional likely-voter model and the other using a modified likely-voter model for an expected higher turnout. For all our composites and Poll Tracker entries, we will be using that second model under the expectation that newly-registered voters and other factors will contribute to a higher turnout this cycle.

Here's our daily composite of the five major national tracking polls. Barack Obama still holds a solid lead over John McCain, with the overall margin is unchanged from yesterday:

• Gallup: Obama 51%, McCain 41%, with a ±2% margin of error, compared to a 50%-43% Obama lead yesterday.

• Rasmussen: Obama 50%, McCain 45%, with a ±2% margin of error, compared to a 51%-45% Obama lead from yesterday.

• Hotline/Diageo: Obama 48%, McCain 42%, with a ±3.4% margin of error, compared to a 49%-41% Obama lead yesterday.

• Research 2000: Obama 52%, McCain 40%, with a ±3% margin of error, compared to a 53%-40% Obama lead from yesterday.

• Zogby: Obama 48%, McCain 44%, with a ±2.9% margin of error, compared to a 49%-43% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.1%-42.5%, a lead of 7.6 points, compared to a 50.4%-42.8% Obama lead yesterday. The undecideds have increased by a total of 0.6%, but it's come equally out of both candidates' scores.

Late Update: Gallup has begun offering two different sub-samples of likely voters, one using a traditional likely-voter model and the other using a new model that has been modified for an expected higher turnout. We will be using that second model, under the expectation that newly-registered voters and other factors will contribute to a higher turnout this cycle. Plugging today's Gallup results for likely voters -- Obama 53%, McCain 43% -- into our calculations yields a revised composite of Obama 50.6%, McCain 43.1%. We'll be switching over to that likely-voter number in our composites from now on.

Here's our daily composite of the five major national tracking polls. Barack Obama's lead may have contracted slightly since yesterday -- but the overall difference is very small, and he remains well ahead:

• Gallup: Obama 50%, McCain 43%, with a ±2% margin of error, compared to a 51%-42% Obama lead yesterday.

• Rasmussen: Obama 51%, McCain 45%, with a ±2% margin of error, compared to a 52%-45% Obama lead from yesterday.

• Hotline/Diageo: Obama 49%, McCain 41%, with a ±3.4% margin of error, compared to a 50%-40% Obama lead yesterday.

• Research 2000: Obama 53%, McCain 40%, with a ±3% margin of error, compared to a 52%-40% Obama lead from yesterday.

• Zogby: Obama 49%, McCain 43%, with a ±2.9% margin of error, compared to a 48%-44% Obama lead yesterday.

Adding these polls together and weighting them by the square roots of their sample sizes, Obama is ahead 50.4%-42.8%, a lead of 7.6 points, compared to a 50.8%-42.5% Obama lead yesterday.

Late Update:Gallup has begun offering two different sub-samples of likely voters, one using a traditional likely-voter model and the other using a new model that has been modified for an expected higher turnout. We will be using that second model, under the expectation that newly-registered voters and other factors will contribute to a higher turnout this cycle. Plugging today's Gallup results for likely voters -- Obama 51%, McCain 45% -- into our calculations yields a revised composite of Obama 50.7%, McCain 43.2%. We'll be switching over to that likely-voter number in our composites from now on.